Recently, a commercial application of electrocatalysis has featured a porous electrode system composed of loosely packed conducting particles such as graphite. See Joseph Haggin, "Trickle-Bed Electrolytic Cell For Peroxide Developed", C & E News, 1984, 62, #11, 16. Haggin describes the use of a porous electrode for large scale production of hydrogen peroxide. The key development in this cell design is the utilization of an electrode material prepared by compressing graphite chips coated with a Teflon-carbon black matrix. Although the "packed-bed" composite fabricated from this procedure provides extended surface area, it does not possess the coherent strength of an integral structural support and is, therefore, subject to mechanical failure.
Electrodes of this kind suffer from several processing disadvantages. Because of path flow impedance, there is a large pressure drop between the inlet and outlet ends of the packed bed systems. The high path flow impedance is derived from a convoluted passageway, which is intrinsic to the packed bed system. This feature inhibits easy access to all of the available electrode surface area.
Another critical disadvantage to the packed-bed system arises from the irregular shape of the spaces between the graphite chips. In a three-phase system, defined herein as a solid electrode in simultaneous contact with a liquid and gas, it has been previously shown that almost all of the Faradaic charge passes through the thinnest portion of the meniscus which is the situs of the three phase system. B. Cahan et al., J. Chem. Phys., 1969, 50, 1307. In a packed-bed system the existence of random and irregular shapes of the passageways precludes control of the charge transfer through manipulation of the meniscus shape.
The art is now replete with various suggestions for electrocatalysts. Spaziante et al., U.S. Pat. No. 4,214,970, discloses electrocatalytic electrodes having an electrically conductive porous base and a electrocatalyst coating. The porous base of this catalyst is disclosed as comprising graphite, carbon strands or sintered metal. There is, however, no teaching for a ceramic substrate having thin walls. Secrist, U.S. Pat. No. 4,484,997, discloses a corrosion-resistant ceramic electrode for the electrowinning of aluminum in Hall-Heroult cells. The ceramic electrode has a conductive ceramic substrate of a base material and at least one additive material which can be diffused from the substrate to the coating by heat treatment. The electrodes characterized in the examples of this patent are Cu/Sb doped SnO.sub.2 anodes.
Ray, U.S. Pat. No. 4,374,761 discloses an inert electrode composition suitable for use in the electrolytic production of metal from a metal compound. The electrode comprises a ceramic oxide composition with a metal powder dispersed through the ceramic composition for purposes of increasing its conductivity.
Despite the commercial success of such catalysts, there is still a need for a catalyst that will accommodate a continuously moving, reaction situs of liquid and gas reactants with a minimal pressure drop. There is also a need for an electrocatalyst exhibiting better efficiency in raw material and energy usage.